1. Field of the Invention
The present invention relates to a method for injecting fluid products into a geological formation, with a view more especially to forming a barrier of these fluids in this formation.
The invention may be advantageously used for example for injecting a plugging product into a geological and more especially an oil-bearing reservoir so as to create a sealed isolating barrier which may be disposed substantially vertically if required.
2. Description of the Prior Art
When using oil recovery methods by injecting gaseous fluids, working of the deposit may use several well lines, each line comprising several wells. When the volume of the deposits between these two well lines has been swept, that is to say when a critical value is reached for the composition of the fluids produced, the injection wells are closed and replaced by the former producing wells.
When starting to work a deposit having a non zero dip, the gaseous fluid is generally injected from the top of the structure so as to obtain an optimum sweep. Thus, a gas cap is created whose volume increases with the advance of the line working of the field.
Because of the dip of the layer, the injection pressure for the gaseous fluid increases when injection is stopped from a first well line and when it is effected from a new well line situated downstream of the dip or downside dip, relatively to the first one.
Thus, a part of the gas injected into this new line serves solely for increasing the pressure in the gas cap so that it reaches the injection pressure. This fraction of the gas is therefore lost and cannot contribute to the efficiency of the sweep. As working of the field advances, the amount of gas thus lost increases considerably.
In addition, the continual increase of the pressure of the gas cap with the depth of the injecting well line may lead to creating a pressure which is too high for the mechanical resistance of the mantel of the deposit. A rupture in this mantel causes considerable losses of gas, adversely affecting the economy of the process and possibly creating considerable pollution. This phenomenon is all the more important the shallower the deposit.
The need to limit these gas losses leads to attempting to isolate, from a certain volume, the gas cap from the rest of the deposit; working would then be continued with the creation of a new gas cap which, when desired, could also be isolated from the unworked part of the deposit.
The prior art may be illustrated by U.S. Pat. Nos. 3,380,522; 4,326,818, and 4,289,354.
The first patent concerns a method for preventing salt water from penetrating into a soft water reservoir. The second patent describes water storage techniques and the third patent teaches a method for working a solid mineral such as coal.
None of these documents relates, in particular, to the formation of a barrier from horizontal drains. Such horizontal drains may be provided by use of apparatus as described in U.S. Pat. No. 4,286,676.